Screenshots showed a tweet which referenced a photograph of former Green Party member.
Midlands-Northwest MEP Luke 'Ming' Flanagan says Belgian Police are investigating how an unauthorised tweet was sent from his Twitter account last week.
Screenshots showed a tweet appearing early on Monday morning which referenced a photograph of former Green Party member, Saoirse McHugh.
The Roscommon MEP says he has now established his account was accessed by a person in Belgium who was using an old password of his.
Flanagan says Belgian police are now trying to figure out the identity of the person who carried out what he has describes as a 'malicious act of vandalism' on his good name.